NBB Nuveen Taxable Municipal Income Fund

RISK FACTORS

Investing in the Common Shares involves risk, including the risk that you may receive little or no return on your investment or that you may lose part or all of your investment. Therefore, before investing in the Common Shares you should consider carefully the following risks, as well as the risk factors set forth under “Risk Factors” beginning on page 9 of the accompanying prospectus.

Investment and Market Risk

An investment in the shares of the Fund is subject to investment risk, including the possible loss of the entire principal amount that you invest. Your investment in shares represents an indirect investment in the municipal securities owned by the Fund. Your shares at any point in time may be worth less than your original investment, even after taking into account the reinvestment of dividends and distributions, if applicable. In addition, the ability of municipalities to collect revenue and service their obligations could be materially and adversely affected by an economic downturn or prolonged recession. Because certain states, including California, New York, Illinois, Texas and Ohio, were heavy issuers of Build America Bonds (“BABs”), the Fund may have a greater exposure to the economic or other factors affecting such states than a more diversified national municipal bond fund. Investors bear a risk of loss to the extent that the price at which they sell their shares is lower than at the time of purchase. The shares of the Fund are designed primarily for long-term investors, and you should not view the Fund as a vehicle for trading purposes.

Market Discount to Net Asset Value

Shares of closed-end investment companies like the Fund have during some periods traded at prices higher than NAV and have during other periods traded at prices lower than NAV. The Fund cannot predict whether Common Shares will trade at, above or below NAV. This characteristic is a risk separate and distinct from the risk that the Fund’s NAV could decrease as a result of investment activities. Investors bear a risk of loss to the extent that the price at which they sell their shares is lower in relation to the Fund’s NAV than at the time of purchase, assuming a stable NAV. Proceeds from the sale of Common Shares in this offering will be reduced by shareholder transaction costs (if applicable, which vary depending on the offering method used). The NAV per Common Share will be reduced by an amount up to the offering costs (estimated to be an additional 0.09% of the offering price assuming a Common Share offering price of $15.97 (the Fund’s closing price on the NYSE on January 3, 2023)). The NAV per Common Share will be reduced by costs associated with any future offerings of Common Shares. Depending on the premium of Common Shares at the time of any offering of Common Shares hereunder, the Fund’s NAV may be reduced by an amount up to the offering costs. The Common Shares are designed primarily for long-term investors, and you should not view the Fund as a vehicle for trading purposes.

Tax Risk

To qualify for the favorable U.S. federal income tax treatment generally accorded to a regulated investment company under Subchapter M of the Code the Fund must, among other requirements, derive in each taxable year at least 90% of its gross income from certain prescribed sources and satisfy a diversification test on a quarterly basis. If the Fund fails to satisfy the qualifying income or diversification requirements in any taxable year, the Fund may be eligible for relief provisions if the failures are due to reasonable cause and not willful neglect and if a penalty tax is paid with respect to

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each failure to satisfy the applicable requirements. Additionally, relief is provided for certain de minimis failures of the diversification requirements where the Fund corrects the failure within a specified period. In order to be eligible for the relief provisions with respect to a failure to meet the diversification requirements, the Fund may be required to dispose of certain assets. If these relief provisions were not available to the Fund and it were to fail to qualify for treatment as a regulated investment company for a taxable year, all of its taxable income (including its net capital gain) would be subject to tax at the 21% regular corporate rate without any deduction for distributions to shareholders, and such distributions would be taxable as ordinary dividends to the extent of the Fund’s current and accumulated earnings and profits.

Leverage Risk

The use of leverage creates special risks for Common Shareholders, including the likelihood of greater volatility of NAV and market price of, and distributions on, the Common Shares than a comparable portfolio without leverage. The use of leverage in a declining market will likely cause a greater decline in Common Share NAV, which may result in a greater decline of the Common Share price, than if the Fund were not to have used leverage.

Leverage risk is the risk associated with the use of borrowings, the issuance of preferred shares or the use of inverse floating rate securities to leverage the common shares. There can be no assurance that the Fund’s leveraging strategy will be successful. Through the use of leverage, the Fund seeks to enhance potential common share earnings over time by typically sourcing leverage with costs based upon short-term interest rates and investing at long-term municipal rates which are typically, although not always, higher. Because the long-term municipal securities in which the Fund invests generally pay fixed rates of interest while the Fund’s costs of leverage generally fluctuate with short- to intermediate-term yields, the incremental earnings from leverage will vary over time. However, the Fund may use derivatives, such as interest rate swaps, to fix the effective rate paid on all or a portion of the Fund’s leverage in an effort to lower leverage costs over an extended period. Accordingly, the Fund cannot assure you that the use of leverage will result in a higher yield or return to Common Shareholders. The income benefit from leverage will be reduced (increased) to the extent that the difference narrows (widens) between the net earnings on the Fund’s portfolio securities and its cost of leverage. If short-or intermediate-term rates rise and the Fund leverage costs fluctuate, the Fund’s cost of leverage could exceed the fixed rate of return on long-term bonds held by the Fund that were acquired during periods of lower interest rates, reducing returns to common shareholders. This could occur even if short- or intermediate-term and long-term municipal rates rise.

The Fund will pay (and Common Shareholders will bear) any costs and expenses relating to the Fund’s use of leverage, which will result in a reduction in the NAV of and net income payable with respect to the Common Shares. Because of the costs of leverage, the Fund may incur losses even if the Fund has positive returns if such returns are not sufficient to cover the costs of leverage.

Nuveen Fund Advisors, based on its assessment of market conditions, may increase or decrease the Fund’s level of leverage or change the types of leverage employed. Such changes may impact the Fund’s distributions and the valuation of the common shares in the secondary market. There can be no assurance that the Fund will continue to utilize leverage or that the Fund’s use of leverage will be successful. Furthermore, the amount of fees paid to Nuveen Fund Advisors and Nuveen Asset Management for investment advisory services will be higher if the Fund uses leverage because the fees will be calculated based on the Fund’s Managed Assets, which may create an incentive for Nuveen Fund Advisors and Nuveen Asset Management to leverage the Fund or increase the Fund’s leverage.

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Certain types of leverage used by the Fund may result in the Fund being subject to certain covenants, asset coverage or other portfolio composition limits by its lenders, Preferred Share purchasers, liquidity providers, rating agencies that may rate the preferred securities, or reverse repurchase counterparties. Such limitations may be more stringent than those imposed by the 1940 Act and may affect whether the Fund is able to maintain its desired amount of leverage. See “Use of Leverage.”

The Fund is required to maintain certain regulatory and rating agency asset coverage requirements in connection with its use of leverage, in order to be able to maintain the ability to declare and pay Common Share distributions. A NRSRO could downgrade its ratings on the Fund’s outstanding preferred shares. A ratings downgrade of the Fund’s preferred shares may result in higher dividend rates and may also force the redemption of such preferred shares at what might be an inopportune time in the market. These factors may result in reduced net earnings or returns to Common Shareholders.

In order to maintain required asset coverage levels, the Fund may be required to alter the composition of its investment portfolio or take other actions, such as redeeming preferred shares or prepaying borrowings with the proceeds from portfolio transactions, at what might be an inopportune time in the market. Such actions could reduce the net earnings or returns to Common Shareholders over time. NRSRO ratings of the Fund’s outstanding preferred shares neither eliminate nor mitigate the risks of investing in Common Shares.

The Fund may invest in the securities of other investment companies, which may themselves be leveraged and therefore present similar risks to those described above. In addition, any investment by the Fund in leveraged investment companies would magnify the Fund’s leverage risk.

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For a more complete description of the Annual Expenses a common shareholder would bear directly or indirectly, see “Management of the Fund—Investment Management and Sub-Advisory Agreements” in the prospectus.

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Examples

The following examples illustrate the expenses including the applicable transaction fees (referred to as the “Maximum Sales Charge” in the fee table above), if any, and estimated offering costs of $0.90, that a common shareholder would pay on a $1,000 investment that is held for the time periods provided in the table. Each example assumes that all dividends and other distributions are reinvested in the Fund and that the Fund’s Annual Total Expenses, as provided above, remain the same. The examples also assume a 5% annual return.¹

Example # 1 (At-the-Market Transaction)

The following example assumes a transaction fee of 1.00%, as a percentage of the offering price.

Example # 2 (Underwritten Transaction)

The following example assumes a transaction fee of 4.00%, as a percentage of the offering price.

Example # 3 (Privately Negotiated Transaction)

The following example assumes there is no transaction fee.

The examples should not be considered a representation of future expenses. Actual expenses may be greater or less than those shown above.

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FINANCIAL HIGHLIGHTS

The following Financial Highlights table is intended to help a prospective investor understand the Fund’s financial performance for the periods shown. Certain information reflects financial results for a single Common Share of the Fund. The total returns in the table represent the rate an investor would have earned or lost on an investment in Common Shares of the Fund (assuming reinvestment of all dividends). The Fund’s annual financial statements and financial highlights as of and for the fiscal years ended March 31, 2022, 2021, 2020, 2019, 2018, 2017, 2016 and 2015, including the financial highlights for the fiscal years then ended, have been audited by KPMG LLP (“KPMG”), an independent registered public accounting firm. KPMG has not reviewed or examined any records, transactions or events after the date of such reports. The information with respect to the fiscal periods ended prior to March 31, 2015 has been audited by other auditors. The information with respect to the six months ended September 30, 2022 is unaudited and is included in the Fund’s 2022 Semi-Annual Report which is incorporated herein by reference. A copy of the Fund’s Annual and Semi-Annual Reports may be obtained from www.sec.gov or by visiting www.nuveen.com. The information contained in, or that can be accessed through, the Fund’s websites is not part of this prospectus, except to the extent specifically incorporated by reference in the SAI. Past results are not indicative of future performance.

The following per share data and ratios have been derived from information provided in the financial statements.

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Selected data for a Common Share outstanding throughout each period:

RISK FACTORS

Investing in the Securities involves risk, including the risk that you may receive little or no return on your investment or that you may lose part or all of your investment. The following discussion, together with the risk factors included in the applicable prospectus supplement, describes the principal risks associated with an investment in the Common Shares and Preferred Shares of the Fund.

Portfolio Level Risks

Municipal Securities Market Risk

Investing in the municipal securities market involves certain risks. The municipal securities market is one in which dealer firms make markets in bonds on a principal basis using their proprietary capital, and during periods of market turmoil these firms’ capital may be severely constrained. As a result, under such conditions, some firms may be unwilling to commit their capital to purchase and to serve as a dealer for municipal securities. The amount of public information available about the municipal securities in the Fund’s portfolio is generally less than that for corporate equities or bonds, and the Fund’s investment performance may therefore be more dependent on the analytical abilities of the Adviser and the Sub-Adviser than if the Fund were to invest in stocks or taxable bonds. The secondary market for municipal securities, particularly the below-investment-grade securities in which the Fund may invest, also tends to be less well-developed or liquid than many other securities markets, which may adversely affect the Fund’s ability to sell its municipal securities at attractive prices or at prices approximating those at which the Fund values them from time to time. Municipal securities may contain redemption provisions, which may allow the securities to be called or redeemed prior to their stated maturity, potentially resulting in the distribution of principal and a reduction in subsequent interest distributions.

The ability of municipal issuers to make timely payments of interest and principal may be diminished during general economic downturns and as governmental cost burdens are reallocated among federal, state and local governments. In addition, laws enacted in the future by Congress or state legislatures or by referenda could extend the time for payment of principal and/or interest or impose other constraints on the enforcement of such obligations or on the ability of municipalities to levy taxes. Further, some state and local governments have been and in the future may be subject to direct ballot referenda that could limit their financial flexibility, or their ability to levy taxes or raise tax revenues, which may adversely affect the marketability of notes and bonds issued by those state and local governments. Issuers of municipal securities might seek protection under the bankruptcy laws. In the event of bankruptcy of such an issuer, the Fund could experience delays in collecting principal and interest and the Fund may not, in all circumstances, be able to collect all principal and interest to which it is entitled. To enforce its rights in the event of a default in the payment of interest or repayment of principal, or both, the Fund may take possession of and manage the assets securing the issuer’s obligations on such securities, which may increase the Fund’s operating expenses. Any income derived from the Fund’s ownership or operation of such assets may not be of the type that would allow the Fund to continue to qualify as a regulated investment company for federal income tax purposes.

Revenue bonds issued by state or local agencies to finance the development of low-income, multi-family housing involve special risks in addition to those associated with municipal securities generally, including that the underlying properties may not generate sufficient income to pay expenses

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and interest costs. These bonds are generally non-recourse against the property owner, may be junior to the rights of others with an interest in the properties, may pay interest the amount of which changes based in part on the financial performance of the property, may be pre-payable without penalty and may be used to finance the construction of housing developments that, until completed and rented, do not generate income to pay interest. Additionally, unusually high rates of default on the underlying mortgage loans may reduce revenues available for the payment of principal or interest on such mortgage revenue bonds.

The outbreak of the novel coronavirus, known as COVID-19, in December 2019, and the resulting pandemic, has adversely impacted global commercial activity and has contributed to significant volatility in certain financial markets, including the municipal bond market. See “—Other Risks—Global Economic Risk”. Due to the COVID-19 pandemic, the risks of the municipal securities market have been magnified. These risks have had, and will continue to have, a material adverse impact on local economies and therefore on the governments in those localities. These risks may also adversely affect several sectors of the municipal bond market, such as retirement facilities, transportation facilities such as airports, hospitals and colleges, among many others. All this has adversely affected the municipal securities market, and may continue to do so for an extended period.

Special Risks Related to Certain Municipal Obligations

Municipal leases and certificates of participation involve special risks not normally associated with general obligations or revenue bonds. Leases and installment purchase or conditional sale contracts (which normally provide for title to the leased asset to pass eventually to the governmental issuer) have evolved as a means for governmental issuers to acquire property and equipment without meeting the constitutional and statutory requirements for the issuance of debt. The debt issuance limitations are deemed to be inapplicable because of the inclusion in many leases or contracts of “non-appropriation” clauses that relieve the governmental issuer of any obligation to make future payments under the lease or contract unless money is appropriated for such purpose by the appropriate legislative body on a yearly or other periodic basis. In addition, such leases or contracts may be subject to the temporary abatement of payments in the event that the governmental issuer is prevented from maintaining occupancy of the leased premises or utilizing the leased equipment. Although the obligations may be secured by the leased equipment or facilities, the disposition of the property in the event of non-appropriation or foreclosure might prove difficult, time consuming and costly, and may result in a delay in recovering or the failure to fully recover the Fund’s original investment. In the event of non-appropriation, the issuer would be in default and taking ownership of the assets may be a remedy available to the Fund, although the Fund does not anticipate that such a remedy would normally be pursued. To the extent that the Fund invests in unrated municipal leases or participates in such leases, the credit quality rating and risk of cancellation of such unrated leases will be monitored on an ongoing basis. Certificates of participation, which represent interests in unmanaged pools of municipal leases or installment contracts, involve the same risks as the underlying municipal leases. In addition, the Fund may be dependent upon the municipal authority issuing the certificates of participation to exercise remedies with respect to the underlying securities. Certificates of participation also entail a risk of default or bankruptcy, both of the issuer of the municipal lease and also the municipal agency issuing the certificate of participation.

Build America Bonds Risk

Build America Bonds are taxable municipal obligations issued pursuant to the American Recovery and Reinvestment Act of 2009 that are subject to federal subsidies of up to 35% of the

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interest payable on the bonds in the form of direct subsidies to the bond issuer or refundable tax credits to the bond holder. Build America Bonds are not guaranteed by the U.S. government or its agencies or instrumentalities. While the federal subsidy continues for the life of the bonds, provided that the issuer continues to meet all applicable program eligibility requirements, there is no assurance that the federal subsidy will be continued at original levels. Under the sequestration process under the Budget Control Act of 2011, automatic spending cuts that became effective on March 1, 2013 reduced the federal subsidy for BABs and other subsidized taxable municipal bonds. The reduced federal subsidy has been extended through 2024. The subsidy payments were reduced by 6.6% in 2018 and 6.2% in 2019. Further decreases in the level of the subsidy may impair the ability of issuers to make interest payments when due.

Build America Bonds were an alternative form of financing to state and local governments whose primary means for accessing the capital markets had been through issuance of tax free municipal bonds. Pursuant to the terms of the American Recovery and Reinvestment Act of 2009, the issuance of Build America Bonds ceased on December 31, 2010. As a result, the availability of such bonds is limited and there can be no assurance that Build America Bonds will be actively traded. The market for the bonds and/or their liquidity may be negatively affected. Changes to the U.S. federal income tax laws that take effect in 2018 may affect the demand for and supply of taxable municipal bonds, including BABs.

Build America Bonds involve similar risks as traditional municipal bonds, including credit and market risk. Because certain states, including California, New York, Illinois, Texas and Ohio, were heavy issuers of BABs, the Fund may have a greater exposure to the economic or other factors affecting such states than a more diversified national municipal bond fund. In addition, should a Build America Bond’s issuer fail to continue to meet the applicable requirements, it is possible that such issuer may not receive federal cash subsidy payments, impairing the issuer’s ability to make scheduled interest payments. Build America Bonds may be subject to greater reinvestment risk, which is the risk that the Fund is unable to invest in bonds with similar yields, as BABs with attractive above-market purchase yields mature or are called.

Interest Rate Risk

Generally, when market interest rates rise, bond prices fall, and vice versa. Interest rate risk is the risk that the municipal securities in the Fund’s portfolio will decline in value because of increases in market interest rates. As interest rates decline, issuers of municipal securities may prepay principal earlier than scheduled, forcing the Fund to reinvest in lower yielding securities and potentially reducing the Fund’s income. As interest rates increase, slower-than-expected principal payments may extend the average life of securities, potentially locking-in a below-market interest rate and reducing the Fund’s value. In typical market interest rate environments, the prices of longer-term municipal securities generally fluctuate more than prices of shorter-term municipal securities as interest rates change. Because the Fund primarily invests in longer-term municipal securities, the common share NAV and market price per share will fluctuate more in response to changes in market interest rates than if the Fund invested primarily in shorter-term municipal securities. Because the values of lower-rated and comparable unrated debt securities are affected both by credit risk and interest rate risk, the price movements of such lower grade securities typically have not been highly correlated to the fluctuations of the prices of investment-grade-quality securities in response to changes in market interest rates. The Fund’s use of leverage, as described herein, will tend to increase common share interest rate risk. There may be less governmental intervention in the securities markets in the near future. The negative impact on fixed-income securities if interest rates increase as a result could negatively impact the Fund’s NAV.

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Municipal Bond Market Liquidity Risk

Inventories of municipal bonds held by brokers and dealers have decreased in recent years, lessening their ability to make a market in these securities. This reduction in market making capacity has the potential to decrease the Fund’s ability to buy or sell bonds, and increase bond price volatility and trading costs, particularly during periods of economic or market stress. In addition, recent changes to federal banking regulations may cause certain dealers to reduce their inventories of municipal bonds, which may further decrease the Fund’s ability to buy or sell bonds. As a result, the Fund may be forced to accept a lower price to sell a security, to sell other securities to raise cash, or to give up an investment opportunity, any of which could have a negative effect on performance. If the Fund needed to sell large blocks of bonds, those sales could further reduce the bonds’ prices and hurt performance.

Credit Risk

Credit risk is the risk that one or more municipal securities in the Fund’s portfolio will decline in price, or the issuer thereof will fail to pay interest or principal when due, because the issuer of the security experiences a decline in its financial status. In general, lower-rated municipal securities carry a greater degree of risk that the issuer will lose its ability to make interest and principal payments, which could have a negative impact on the Fund’s NAV or dividends. Credit risk is increased when a portfolio security is downgraded or the perceived creditworthiness of the issuer deteriorates. If a municipal security satisfies the rating requirements described above at the time of investment and is subsequently downgraded below that rating, the Fund will not be required to dispose of the security. If a downgrade occurs, Nuveen Asset Management will consider what action, including the sale of the security, is in the best interests of the Fund and its shareholders. This means that the Fund may invest in municipal securities that are involved in bankruptcy or insolvency proceedings or are experiencing other financial difficulties at the time of acquisition (such securities are commonly referred to as distressed securities).

Below Investment Grade Risk

Municipal securities of below investment grade quality, commonly referred to as junk bonds, are regarded as having predominately speculative characteristics with respect to capacity to pay interest and repay principal when due, and are susceptible to default or decline in market value due to adverse economic and business developments. Also, to the extent that the rating assigned to a municipal security in the Fund’s portfolio is downgraded by any NRSRO, the market price and liquidity of such security may be adversely affected. The market values for municipal securities of below investment grade quality tend to be volatile, and these securities are less liquid than investment grade municipal securities. For these reasons, an investment in the Fund, compared with a portfolio consisting solely of investment grade securities, may experience the following:

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Adverse changes in economic conditions are more likely to lead to a weakened capacity of a below investment grade issuer to make principal payments and interest payments compared to an investment grade issuer. The principal amount of below investment grade securities outstanding has proliferated in the past decade as an increasing number of issuers have used below investment grade securities for financing. The current downturn may severely affect the ability of highly leveraged issuers to service their debt obligations or to repay their obligations upon maturity. As the national economy experiences the current economic downturn, resulting in decreased tax and other revenue streams of municipal issuers, or in the event interest rates rise sharply, increasing the interest cost on variable rate instruments and negatively impacting economic activity, the number of defaults by below investment grade municipal issuers is likely to increase. Similarly, downturns in profitability in specific industries could adversely affect private activity bonds. The market values of lower quality debt securities tend to reflect individual developments of the issuer to a greater extent than do higher quality securities, which react primarily to fluctuations in the general level of interest rates. Factors having an adverse impact on the market value of lower quality securities may have an adverse impact on the Fund’s NAV and the market value of its Common Shares. In addition, the Fund may incur additional expenses to the extent it is required to seek recovery upon a default in payment of principal or interest on its portfolio holdings. In certain circumstances, the Fund may be required to foreclose on an issuer’s assets and take possession of its property or operations. In such circumstances, the Fund would incur additional costs in disposing of such assets and potential liabilities from operating any business acquired.

The secondary market for below investment grade securities may not be as liquid as the secondary market for more highly rated securities, a factor that may have an adverse effect on the Fund’s ability to dispose of a particular security. There are fewer dealers in the market for below investment grade municipal securities than the market for investment grade municipal securities. The prices quoted by different dealers for below investment grade municipal securities may vary significantly, and the spread between the bid and ask price is generally much larger for below investment grade municipal securities than for higher quality instruments. Under adverse market or economic conditions, the secondary market for below investment grade securities could contract further, independent of any specific adverse changes in the condition of a particular issuer, and these instruments may become illiquid. As a result, the Fund could find it more difficult to sell these securities or may be able to sell the securities only at prices lower than if such securities were widely traded. Prices realized upon the sale of such lower rated or unrated securities, under these circumstances, may be less than the prices used in calculating the Fund’s NAV.

Issuers of below investment grade securities are highly leveraged and may not have available to them more traditional methods of financing. Therefore, the risk associated with acquiring the securities of such issuers generally is greater than is the case with higher rated securities. For example, during an economic downturn or a sustained period of rising interest rates, highly leveraged issuers of below investment grade securities may experience financial stress. During such periods, such issuers may not have sufficient revenues to meet their interest payment obligations. The issuer’s ability to service its debt obligations also may be adversely affected by specific developments, the issuer’s inability to meet specific projected forecasts or the unavailability of additional financing. The risk of loss from default by the issuer is significantly greater for the holders of below investment grade securities because such securities are generally unsecured and are often subordinated to other creditors of the issuer. Prices and yields of below investment grade securities will fluctuate over time and, during periods of economic uncertainty, volatility of below investment grade securities may adversely affect the Fund’s NAV. In addition, investments in below investment grade zero coupon bonds rather than income-bearing below investment grade securities, may be more speculative and may be subject to greater fluctuations in value due to changes in interest rates.

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The Fund may invest in the securities of an issuer which, at the time of investment, is in default on its obligations to pay principal or interest thereon when due or that is involved in a bankruptcy proceeding (i.e., rated below C- at the time of investment), and may invest in municipal securities that are experiencing other financial difficulties at the time of acquisition (such securities are commonly referred to as distressed securities). The issuers of such securities may be in transition, out of favor, financially leveraged or troubled, or potentially troubled, and may be or have recently been involved in major strategic actions, restructurings, bankruptcy, reorganization or liquidation. These characteristics of these companies can cause their securities to be particularly risky, although they also may offer the potential for high returns. These companies’ securities may be considered speculative, and the ability of the companies to pay their debts on schedule could be affected by adverse interest rate movements, changes in the general economic climate, economic factors affecting a particular industry or specific developments within the companies. Distressed securities frequently do not produce income while they are outstanding and may require the Fund to bear certain extraordinary expenses in order to protect and recover its investment.

Income Risk

The Fund’s income is based primarily on the interest it earns from its investments, which can vary widely over the short term and long term. If interest rates drop, the Fund’s income available over time to make dividend payments could drop as well if the Fund purchases securities with lower interest coupons.

Call Risk or Prepayment Risk

During periods of declining interest rates or for other purposes, issuers of callable bonds with higher interest coupons may exercise their option to “call” (or prepay) bonds before their maturity date, forcing the Fund to reinvest in lower yielding securities.

Reinvestment Risk

Reinvestment risk is the risk that the income from the Fund’s portfolio will decline if and when the Fund invests the proceeds from matured, traded or called bonds at market interest rates that are below the current earnings rate of the Fund’s portfolio. A decline in income could affect the ability of the Fund to pay dividends on its common shares, as well as the common shares’ market price or overall returns.

Inverse Floating Rate Securities Risk

Typically, inverse floating rate securities represent beneficial interests in TOB trusts that hold municipal bonds. In general, income on inverse floating rate securities will decrease when interest rates increase and increase when interest rates decrease. Investments in inverse floating rate securities may subject the Fund to the risks of reduced or eliminated interest payments and losses of principal in respect of the underlying municipal bonds.

In the case of certain TOB trusts, neither the holders of the associated floating rate securities nor the TOB trust itself have recourse to the holder of the inverse floating rate securities for losses on the underlying municipal bonds. In that case, the risk of loss to the Fund generally is limited to its investment in such securities. However, in certain circumstances and in the Sub-Adviser’s discretion,

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the Fund may enter into a recourse arrangement with the liquidity provider to a TOB trust in the form of a separate shortfall and forbearance agreement by which the Fund will agree to reimburse the liquidity provider for any amounts paid by it under the liquidity facility. The Fund may enter into such recourse agreements: (1) when the liquidity provider to the TOB trust requires such an agreement because the level of leverage in the trust exceeds the level that the liquidity provider is willing to support absent such an agreement; and/or (2) to seek to prevent the liquidity provider from collapsing the trust in the event that the underlying municipal bond held in the trust has declined in value to the point where it may cease to exceed the face amount of outstanding short-term floaters. Such an agreement would require the Fund to reimburse the liquidity provider, among other amounts, upon termination of the TOB trust for the shortfall of the liquidation value of the bonds held in the trust relative to the amount of principal and unpaid interest due to the holders of floating rate securities. In such instances, the Fund may be at risk of loss that exceeds its investment in the inverse floating rate securities.

Inverse floating rate securities may increase or decrease in value at a greater rate than the underlying municipal bonds, which effectively leverages the Fund’s investment. As a result, the market value of such securities generally will be more volatile than that of otherwise comparable municipal bonds held on an unleveraged basis outside a TOB trust.

The Fund may invest in inverse floating rate securities issued by TOB trusts in which the liquidity provider has recourse to the Fund (a “recourse TOB trust”) to the extent that the value of the bonds deposited in the TOB trust may fall in value below the principal amount of the short-term floating rate securities issued by that trust. The inverse floating rate securities issued by such recourse TOB trusts may be highly leveraged. The structure and degree to which the Fund’s inverse floating rate securities are highly leveraged will vary based upon a number of factors, including the size of the trust itself and the terms of the underlying municipal bonds. An inverse floating rate security generally is considered highly leveraged if the ratio of (1) the principal amount of the short-term floating rate securities issued by the TOB trust to (2) the principal amount of that TOB trust’s inverse floating rate securities equals or exceeds 3:1. In the event of a significant decline in the value of an underlying municipal bond held in a recourse TOB trust, the Fund may suffer losses in excess of the amount of its investment in the inverse floating securities (typically up to an amount equal to the outstanding face amount of such municipal bonds) as a result of liquidating the trust.

The Fund’s investment in inverse floating rate securities will create effective leverage, used in pursuit of increased common share net income and returns. But such effective leverage could reduce common share income (such as if the interest rate paid on the short-term floating rate securities were to exceed the interest rate being received on the municipal bonds underlying the TOB trust, net of trust expenses, for a meaningful period of time), and could also diminish common share long-term returns (such as if the value of the municipal bonds underlying the TOB trust were to decline in value by more than any positive differential between the income being earned on those underlying bonds, net of trust expenses, relative to the interest being paid to the holders of the short-term floating rate securities issued by that trust).

The amount of fees paid to the Adviser (which in turn pays a portion of its fees to the Sub-Adviser) for investment advisory services will be higher when the Fund uses leverage because the advisory fees are calculated based on the Fund’s managed assets. This may create an incentive for the Adviser and/or the Sub-Adviser to leverage the Fund.

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Inverse floating rate securities have varying degrees of liquidity based, among other things, upon the liquidity of the underlying municipal bonds deposited in the TOB trust.

The leverage attributable to inverse floating rate securities may be “called away” on relatively short notice and therefore may be less permanent than more traditional forms of leverage. In certain circumstances, the likelihood of an increase in the volatility of NAV and market price of the common shares may be greater for the Fund that relies primarily on inverse floating rate securities to achieve a desired effective leverage ratio. The Fund may be required to sell its inverse floating rate securities at less than favorable prices or to liquidate other Fund portfolio holdings in certain circumstances, including, but not limited to, the following:

There is no assurance that the Fund’s strategy of investing in inverse floating rate securities will be successful.

Reverse Repurchase Agreement Risk

Reverse repurchase agreements involve the sale of securities held by the Fund with an agreement to repurchase the securities at an agreed-upon price, date and interest payment, and represent borrowings of the Fund. Reverse repurchase agreements involve the risk that the other party to the agreement may fail to return the securities in a timely manner or at all. The Fund could lose money if it is unable to recover the securities and the value of the collateral held by the Fund, including the value of investments made with cash collateral, is less than the value of the securities. These events could also trigger adverse tax consequences to the Fund. The use by the Fund of reverse repurchase agreements involves many of the same risks of leverage since the proceeds derived from such reverse repurchase agreements may be invested in additional securities.

Insurance Risk

The Fund may purchase municipal securities that are secured by insurance, bank credit agreements or escrow accounts. The credit quality of the companies that provide such credit enhancements will affect the value of those securities. During and following the 2007–2009 financial crisis, certain significant providers of insurance for municipal securities incurred significant losses as a result of exposure to sub-prime mortgages and other lower credit quality investments that experienced defaults or otherwise suffered extreme credit deterioration. Such losses reduced the insurers’ capital and called into question their continued ability to perform their obligations under such insurance should they be called upon to do so. While an insured municipal security will typically be deemed to have the rating of its insurer, if the insurer of a municipal security suffers a downgrade in its credit rating or the market discounts the value of the insurance provided by the insurer, the rating of the underlying municipal security will be more relevant and the value of the municipal security would more closely, if not entirely, reflect such rating. In such a case, the value of insurance associated with a

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municipal security would decline and may not add any value. The insurance feature of a municipal security does not guarantee the full payment of principal and interest through the life of an insured obligation, the market value of the insured obligation or the NAV of the common shares represented by such insured obligation.

Tax Risk

To qualify for the favorable U.S. federal income tax treatment generally accorded to a regulated investment company under Subchapter M of the Code the Fund must, among other requirements, derive in each taxable year at least 90% of its gross income from certain prescribed sources and satisfy a diversification test on a quarterly basis. If the Fund fails to satisfy the qualifying income or diversification requirements in any taxable year, the Fund may be eligible for relief provisions if the failures are due to reasonable cause and not willful neglect and if a penalty tax is paid with respect to each failure to satisfy the applicable requirements. Additionally, relief is provided for certain de minimis failures of the diversification requirements where the Fund corrects the failure within a specified period. In order to be eligible for the relief provisions with respect to a failure to meet the diversification requirements, the Fund may be required to dispose of certain assets. If these relief provisions were not available to the Fund and it were to fail to qualify for treatment as a regulated investment company for a taxable year, all of its taxable income (including its net capital gain) would be subject to tax at the 21% regular corporate rate without any deduction for distributions to shareholders, and such distributions would be taxable as ordinary dividends to the extent of the Fund’s current and accumulated earnings and profits.

Inflation Risk

Inflation is the reduction in the purchasing power of money resulting from the increase in the price of goods and services. Inflation risk is the risk that the inflation-adjusted (or “real”) value of assets or income from investment will be worth less in the future. As inflation increases, the real value of common shares and distributions can decline. In addition, during any period of rising inflation, interest rates on borrowings would likely increase, which would tend to further reduce returns to common shareholders.

Deflation Risk

Deflation risk is the risk that prices throughout the economy decline over time—the opposite of inflation risk. Deflation may have an adverse effect on the creditworthiness of issuers and may make issuer default more likely, which may result in a decline in the value of the Fund’s portfolio.

Derivatives Risk, Including the Risk of Swaps

The Fund’s use of derivatives involves risks different from, and possibly greater than, the risks associated with investing directly in the investments underlying the derivatives, including: the imperfect correlation between the value of such instruments and the underlying assets of the Fund, which creates the possibility that the loss on such instruments may be greater than the gain in the value of the underlying assets in the Fund’s portfolio; the loss of principal; the possible default of the other party to the transaction; and illiquidity of the derivative investments. If the Fund enters into certain derivatives transactions, it could lose more than the principal amount invested. Whether the Fund’s use of derivatives is successful will depend on, among other things, if the Adviser and/or the Sub-Adviser

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correctly forecast market values, interest rates and other applicable factors. If the Adviser and/or the Sub-Adviser incorrectly forecast these and other factors, the investment performance of the Fund will be unfavorably affected.

The Fund may enter into debt-related derivative instruments including credit default swap contracts and interest rate swaps. Like most derivative instruments, the use of swaps is a highly specialized activity that involves investment techniques and risks different from those associated with ordinary portfolio securities transactions. In addition, the use of swaps requires an understanding by the Adviser and/or the Sub-Adviser of not only the referenced asset, rate or index, but also of the swap itself. The derivatives markets are subject to a changing regulatory environment. It is possible that regulatory or other developments in the derivatives markets could adversely affect the Fund’s ability to successfully use derivative instruments.

Furthermore, derivative investments may be illiquid. Although both OTC and exchange-traded derivatives markets may experience a lack of liquidity, OTC non-standardized derivatives transactions are generally less liquid than exchange-traded instruments. The illiquidity of the derivatives markets may be due to various factors, including congestion, disorderly markets, limitations on deliverable supplies, the participation of speculators, government regulation and intervention, and technical and operational or system failures. In addition, the liquidity of a secondary market in an exchange-traded derivative contract may be adversely affected by “daily price fluctuation limits” established by the exchanges which limit the amount of fluctuation in an exchange-traded contract price during a single trading day. Once the daily limit has been reached in the contract, no trades may be entered into at a price beyond the limit, thus preventing the liquidation of open positions. Prices have in the past moved beyond the daily limit on a number of consecutive trading days. If it is not possible to close an open derivative position entered into by the Fund, the Fund would continue to be required to make cash payments of variation (or mark-to-market) margin in the event of adverse price movements. In such a situation, if the Fund has insufficient cash, it may have to sell portfolio securities to meet variation margin requirements at a time when it may be disadvantageous to do so. The absence of liquidity may also make it more difficult for the Fund to ascertain a market value for such instruments. The inability to close futures or derivatives positions also could have an adverse impact on the Fund’s ability to effectively hedge its portfolio.

Derivatives Regulatory Risk

Future regulatory developments could impact the Fund’s ability to invest in certain derivatives. It is possible that government regulation of various types of derivative instruments, including futures, options and swap agreements, may limit or prevent the Fund from using such instruments as a part of its investment strategies, and could ultimately prevent the Fund from being able to achieve its investment objectives. It is impossible to fully predict the effects of past, present or future legislation and regulation in this area, but the effects could be substantial and adverse. There is a likelihood of future regulatory developments altering, perhaps to a material extent, the nature of an investment in the Fund or the ability of the Fund to continue to implement its investment strategies. It is possible that legislative and regulatory activity could limit or restrict the ability of the Fund to use certain instruments as a part of its investment strategies. Limits or restrictions applicable to the counterparties with which the Fund engages in derivatives transactions (for example, the Volcker Rule) could also prevent the Fund from using certain instruments.

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The Dodd-Frank Act sets forth a regulatory framework for OTC derivatives, including financial instruments, such as swaps, in which the Fund may invest. The Dodd-Frank Act grants significant authority to the SEC and the CFTC to regulate OTC derivatives and market participants and requires clearing and exchange trading of many current OTC derivatives transactions. The implementation of the provisions of the Dodd-Frank Act by the SEC and the CFTC could adversely affect the Fund’s ability to pursue its investment strategies. The Dodd-Frank Act and the rules promulgated thereunder could, among other things, adversely affect the value of the investments held by the Fund, restrict the Fund’s ability to engage in derivatives transactions and/or increase the costs of such derivatives transactions.

Further, in February 2012, the CFTC issued a final rule rescinding and amending certain exemptions from registration requirements under the U.S. Commodity Exchange Act, as amended (the “CEA”), previously available to investment advisers registered with the SEC under the 1940 Act, including the exemption available under CFTC Rule 4.5. In the event that the Fund’s investments in derivative instruments regulated under the CEA, including futures, swaps and options, exceed a certain threshold, the Adviser and/or the Sub-Adviser may be required to register as a “commodity pool operator” and/or a “commodity trading advisor” with the CFTC. In the event the Adviser and/or the Sub-Adviser is required to register with the CFTC, it will become subject to additional recordkeeping and reporting requirements with respect to the Fund, which may increase the Fund’s expenses.

Hedging Risk

The Fund’s use of derivatives or other transactions to reduce risk involves costs and will be subject to the Adviser’s and/or the Sub-Adviser’s ability to predict correctly changes in the relationships of such hedge instruments to the Fund’s portfolio holdings or other factors. No assurance can be given that the Adviser’s and/or the Sub-Adviser’s judgment in this respect will be correct, and no assurance can be given that the Fund will enter into hedging or other transactions at times or under circumstances in which it may be advisable to do so. Hedging activities may reduce the Fund’s opportunities for gain by offsetting the positive effects of favorable price movements and may result in net losses.

Other Investment Companies Risk

An investment in the securities of another investment company will expose the Fund to the risks of investing in the securities held in such other investment company’s portfolio. In addition, the Fund’s shareholders will bear their proportionate share of the fees and expenses of such other investment company in addition to the fees and expenses of the Fund. The securities of other investment companies may also be leveraged. As a result, the Fund may be indirectly exposed to leverage through an investment in such securities. Utilization of leverage is a speculative investment technique and involves certain risks. An investment in securities of other investment companies that are leveraged may expose the Fund to higher volatility in the market value of such securities and the possibility that the Fund’s long-term returns on such securities will be diminished.

Illiquid Securities Risk

Illiquid securities are securities that are not readily marketable and may include restricted securities, which are securities that may not be resold unless they have been registered under the Securities Act of 1933, as amended (the “Securities Act”), or that can be sold in a private transaction

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pursuant to an available exemption from such registration. Illiquid securities involve the risk that the securities will not be able to be sold at the time desired by the Fund or at prices approximating the value at which the Fund is carrying the securities on its books from time to time.

Other Risks

Economic and Political Events Risk

The Fund may be more sensitive to adverse economic, business or political developments if it invests a substantial portion of its assets in the bonds of similar projects (such as those relating to the education, health care, housing, transportation, or utilities industries), industrial development bonds, or in particular types of municipal securities (such as general obligation bonds, private activity bonds or moral obligation bonds). Such developments may adversely affect a specific industry or local political and economic conditions, and thus may lead to declines in the bonds’ creditworthiness and value.

Global Economic Risk

National and regional economies and financial markets are becoming increasingly interconnected, which increases the possibilities that conditions in one country, region or market might adversely impact issuers in a different country, region or market. Changes in legal, political, regulatory, tax and economic conditions may cause fluctuations in markets and prices of investments around the world, which could negatively impact the value of the Fund’s investments. Major economic or political disruptions, particularly in large economies like China’s, may have global negative economic and market repercussions. Additionally, the aftermath of the war in Iraq, instability in Afghanistan, Pakistan, Egypt, Libya, Syria, Russia, Ukraine and the Middle East, natural and environmental disasters and the spread of infectious illnesses or other public health emergencies, possible terrorist attacks in the United States and around the world, continued tensions between North Korea and the United States and the international community generally, growing social and political discord in the United States, the European debt crisis, the response of the international community—through economic sanctions and otherwise—to Russia’s annexation of the Crimea region of Ukraine and posture vis-a-vis Ukraine, further downgrade of U.S. Government securities, the change in the U.S. president and the new administration and other similar events may adversely affect the global economy and the markets and issuers in which the Fund invests. Recent examples of such events include the outbreak of a novel coronavirus known as COVID-19 that was first detected in China in December 2019 and heightened concerns regarding North Korea’s nuclear weapons and long-range ballistic missile programs. These events could reduce consumer demand or economic output, result in market closure, travel restrictions or quarantines, and generally have a significant impact on the economy. These events could also impair the information technology and other operational systems upon which the Fund’s service providers, including Nuveen Asset Management, rely, and could otherwise disrupt the ability of employees of the Fund’s service providers to perform essential tasks on behalf of the Fund.

In December 2019, an initial outbreak of COVID-19 was reported and has resulted in numerous deaths and the imposition of both local and more widespread quarantine measures, border closures and other travel restrictions, causing social unrest and commercial disruption on a global scale. In response to the COVID-19 pandemic, central banks and governments have responded with liquidity injections to ease the strain on financial systems and stimulus measures to buffer the shock to businesses and consumers. These measures have helped stabilize the markets over the short term, but volatility will

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likely remain elevated until the health crisis itself is under control (via fewer new cases, lower infection rates and/or verified treatments). There are still many unknowns and new information is incoming daily, compounding the difficulty of modeling outcomes for epidemiologists and economists alike. Additionally, the recent outbreak of COVID-19 has adversely impacted global commercial activity and has contributed to significant volatility in certain financial markets. There are no comparable recent events in the U.S. that provide guidance as to the effect of the spread of COVID-19 and a pandemic on the economy as a whole and, consequently, the Fund. Accordingly, while there have been proposed, and in some cases enacted, economic stimulus measures aimed at curbing the negative economic impacts to the U.S. and other countries as a result of COVID-19, it cannot be determined at this time whether such stimulus measures will have a stabilizing economic effect.

To the extent the impacts of COVID-19 continue, the Fund may experience negative impacts to its business that could exacerbate other risks to which the Fund is subject, including: (1) issuers of fixed-income investments could be materially impacted by the COVID-19 pandemic, which may, in turn, negatively affect the value of such investments or such issuers’ ability to make interest payments or distributions to the Fund and result in a decrease in the NAV of the Fund; (2) operational impacts on and availability of key personnel of Nuveen Fund Advisors, Nuveen Asset Management, and/or any of the Fund’s other service providers, vendors and counterparties as they face changed circumstances and/or illness related to the pandemic; and (3) limitations on the Fund’s ability to make distributions or dividends, as applicable, to Common Shareholders. The Fund does not know and can not predict how long the securities markets may be affected by these events and the effects of these and similar events in the future on the U.S. economy and securities markets. The Fund may be adversely affected by abrogation of international agreements and national laws which have created the market instruments in which the Fund may invest, failure of the designated national and international authorities to enforce compliance with the same laws and agreements, failure of local, national and international organizations to carry out their duties prescribed to them under the relevant agreements, revisions of these laws and agreements which dilute their effectiveness or conflicting interpretation of provisions of the same laws and agreements.

Governmental and quasi-governmental authorities and regulators throughout the world have in the past responded to major economic disruptions with a variety of significant fiscal and monetary policy changes, including but not limited to, direct capital infusions into companies, new monetary programs and dramatically lower interest rates. An unexpected or quick reversal of these policies, or the ineffectiveness of these policies, could increase volatility in securities markets, which could adversely affect the Fund’s investments. See “—Recent Market Conditions” below.

Recent Market Conditions

In response to the financial crisis and recent market events, the United States and other governments and the Federal Reserve and certain foreign central banks have taken steps to support financial markets. Policy and legislative changes by the United States government and the Federal Reserve to assist in the ongoing support of financial markets, both domestically and in other countries, are changing many aspects of financial regulation. The impact of these changes on the markets, and the practical implications for market participants, may not be fully known for some time. In some countries where economic conditions are recovering, such countries are nevertheless perceived as still fragile. Withdrawal of government support, failure of efforts in response to the crisis, or investor perception that such efforts are not succeeding, could adversely impact the value and liquidity of certain investments. The severity or duration of adverse economic conditions may also be affected by

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policy changes made by governments or quasi-governmental organizations, including changes in tax laws and the imposition of trade barriers. The impact of new financial regulation legislation on the markets and the practical implications for market participants may not be fully known for some time. Changes to the Federal Reserve policy, including with respect to certain interest rates, may affect the value, volatility and liquidity of dividend and interest paying securities. Regulatory changes are causing some financial services companies to exit long-standing lines of business, resulting in dislocations for other market participants. In addition, the contentious domestic political environment, as well as political and diplomatic events within the United States and abroad, such as the U.S. government’s inability at times to agree on a long-term budget and deficit reduction plan, the threat of a federal government shutdown and threats not to increase the federal government’s debt limit, may affect investor and consumer confidence and may adversely impact financial markets and the broader economy, perhaps suddenly and to a significant degree. The U.S. government has recently reduced the federal corporate income tax rate, and future legislative, regulatory and policy changes may result in more restrictions on international trade, less stringent prudential regulation of certain players in the financial markets, and significant new investments in infrastructure and national defense. Markets may react strongly to expectations about the changes in these policies, which could increase volatility, especially if the markets’ expectations for changes in government policies are not borne out.

Changes in market conditions will not have the same impact on all types of investments. Interest rates have been unusually low in recent years in the United States and abroad, but there is a consensus that interest rates will increase during the life of the Fund, which could negatively impact the price of debt securities. Because there is little precedent for this situation, it is difficult to predict the impact of a significant rate increase on various markets. For example, because investors may buy securities or other investments with borrowed money, a significant increase in interest rates may cause a decline in the markets for those investments. Because of the sharp decline in the worldwide price of oil, there is a concern that oil producing nations may withdraw significant assets now held in U.S. Treasuries, which could force a substantial increase in interest rates. Regulators have expressed concern that rate increases may cause investors to sell fixed income securities faster than the market can absorb them, contributing to price volatility. In addition, there is a risk that the prices of goods and services in the United States and many foreign economies may decline over time, known as deflation (the opposite of inflation). Deflation may have an adverse effect on stock prices and creditworthiness and may make defaults on debt more likely. If a country’s economy slips into a deflationary pattern, it could last for a prolonged period and may be difficult to reverse.

On June 23, 2016, the United Kingdom (“UK”) held a referendum on whether to remain a member state of the European Union (“EU”), in which voters favored the UK’s withdrawal from the EU, an event widely referred to as “Brexit” and which triggered a two-year period of negotiations on the terms of withdrawal. The formal notification to the European Council required under Article 50 of the Treaty on EU was made on March 29, 2017, following which the terms of exit were negotiated. On January 31, 2020, the UK formally withdrew from the EU, subject to a transitional period that ended on December 31, 2020. The longer term economic, legal, political and social framework to be put in place between the UK and the EU are unclear at this stage and are likely to lead to ongoing political and economic uncertainty and periods of exacerbated volatility in both the UK and in wider European markets for some time. The outcomes may cause increased volatility and have a significant adverse impact on world financial markets, other international trade agreements, and the UK and European economies, as well as the broader global economy for some time. Additionally, a number of countries in Europe have suffered terror attacks, and additional attacks may occur in the future. Ukraine has experienced ongoing military conflict; this conflict may expand and military attacks could occur

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elsewhere in Europe. Europe has also been struggling with mass migration from the Middle East and Africa. The ultimate effects of these events and other socio-political or geographical issues are not known but could profoundly affect global economies and markets.

The current political climate has intensified concerns about a potential trade war between China and the United States, as each country has recently imposed tariffs on the other country’s products. These actions may trigger a significant reduction in international trade, the oversupply of certain manufactured goods, substantial price reductions of goods and possible failure of individual companies and/or large segments of China’s export industry, which could have a negative impact on the Fund’s performance. U.S. companies that source material and goods from China and those that make large amounts of sales in China would be particularly vulnerable to an escalation of trade tensions. Uncertainty regarding the outcome of the trade tensions and the potential for a trade war could cause the U.S. dollar to decline against safe haven currencies, such as the Japanese yen and the euro. Events such as these and their consequences are difficult to predict and it is unclear whether further tariffs may be imposed or other escalating actions may be taken in the future.

The impact of these developments in the near- and long-term is unknown and could have additional adverse effects on economies, financial markets and asset valuations around the world.

Legislation and Regulatory Risk

At any time after the date of this prospectus, legislation or additional regulations may be enacted that could negatively affect the assets of the Fund, investments held by the Fund or the issuers of such investments. Changing approaches to regulation may have a negative impact on the entities and/or investments in which the Fund invests. Legislation or regulation may also change the way in which the Fund itself is regulated. Fund shareholders may incur increased costs resulting from such legislation or additional regulation. There can be no assurance that future legislation, regulation or deregulation will not have a material adverse effect on the Fund or will not impair the ability of the Fund to achieve its investment objective.

For example, the Dodd-Frank Act is designed to impose stringent regulation on the over-the-counter derivatives market in an attempt to increase transparency and accountability and provides for, among other things, new clearing, execution, margin, reporting, recordkeeping, business conduct, disclosure, position limit, minimum net capital and registration requirements. Although the CFTC has released final rules under the Dodd-Frank Act, many of the provisions are subject to further final rulemaking, and thus the Dodd-Frank Act’s ultimate impact remains unclear.

The SEC recently adopted new Rule 18f-4 under the 1940 Act governing the use of derivatives by registered investment companies, which could affect the nature and extent of derivatives used by the Fund. It is possible that new Rule 18f-4 could limit the implementation of the Fund’s use of derivatives, which could have an adverse impact on the Fund.

Additionally, the Fund is operated by persons who have claimed an exclusion, granted to operators of registered investment companies like the Fund, from registration as a “commodity pool operator” under Rule 4.5 promulgated by the CFTC pursuant to its authority under the Commodity Exchange Act (the “CEA”) and, therefore, is not subject to registration or regulation as a “commodity pool operator.” As a result, the Fund is limited in its ability to use commodity futures (which include futures on broad-based securities indexes and interest rate futures) or options on commodity futures,

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engage in swaps transactions or make certain other investments (whether directly or indirectly through investments in other investment vehicles) for purposes other than bona fide hedging. With respect to transactions other than for bona fide hedging purposes, either: (1) the aggregate initial margin and premiums required to establish the Fund’s positions in such investments may not exceed 5% of the liquidation value of the Fund’s portfolio (after accounting for unrealized profits and unrealized losses on any such investments); or (2) the aggregate net notional value of such instruments, determined at the time the most recent position was established, may not exceed 100% of the liquidation value of the Fund’s portfolio (after accounting for unrealized profits and unrealized losses on any such positions). In addition to meeting one of the foregoing trading limitations, the Fund may not market itself as a commodity pool or otherwise as a vehicle for trading in the futures, options or swaps markets. If the Fund does not continue to claim the exclusion, it would likely become subject to registration and regulation as a commodity pool operator. The Fund may incur additional expenses as a result of the CFTC’s registration and regulatory requirements.

Anti-Takeover Provisions

The Fund’s Declaration of Trust and By-laws include provisions that could limit the ability of other entities or persons to acquire control of the Fund or convert the Fund to open-end status. These provisions could have the effect of depriving the Common Shareholders of opportunities to sell their Common Shares at a premium over the then-current market price of the Common Shares. See “Certain Provisions in the Declaration of Trust and By-Laws.”

Potential Conflicts of Interest Risk

Nuveen Fund Advisors and Nuveen Asset Management each provide a wide array of portfolio management and other asset management services to a mix of clients and may engage in ordinary course activities in which their respective interests or those of their clients may compete or conflict with those of the Fund. In certain circumstances, and subject to its fiduciary obligations under the Investment Advisers Act of 1940, Nuveen Asset Management may have to allocate a limited investment opportunity among its clients, which include closed-end funds, open-end funds and other commingled funds. Nuveen Fund Advisors and Nuveen Asset Management have each adopted policies and procedures designed to address such situations and other potential conflicts of interests.

For additional information about potential conflicts of interest, and the way in which Nuveen Fund Advisors and Nuveen Asset Management address such conflicts, please see “Subadviser—Nuveen Asset Management Conflict of Interest Policies” in the SAI.

The following risks are not considered to be principal risks of investing in the Fund:

Borrowing Risk

In addition to borrowing for leverage (see “Leverage”), the Fund may borrow for temporary or emergency purposes, to pay dividends, repurchase its shares, or clear portfolio transactions. Borrowing may exaggerate changes in the NAV of the Fund’s shares and may affect the Fund’s net income. When the Fund borrows money, it must pay interest and other fees, which will reduce the Fund’s returns if such costs exceed the returns on the portfolio securities purchased or retained with such borrowings. Any such borrowings are intended to be temporary. However, under certain market circumstances, such borrowings might be outstanding for longer periods of time.

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Cybersecurity Risk

Technology, such as the internet, has become more prevalent in the course of business, and as such, the Fund and its service providers are susceptible to operational and information security risk resulting from cyber incidents. Cyber incidents refer to both intentional attacks and unintentional events including: processing errors, human errors, technical errors including computer glitches and system malfunctions, inadequate or failed internal or external processes, market-wide technical-related disruptions, unauthorized access to digital systems (through “hacking” or malicious software coding), computer viruses, and cyber-attacks which shut down, disable, slow or otherwise disrupt operations, business processes or website access or functionality (including denial of service attacks). Cyber incidents could adversely impact the Fund and cause the Fund to incur financial loss and expense, as well as face exposure to regulatory penalties, reputational damage, and additional compliance costs associated with corrective measures. Cyber incidents may cause the Fund or its service providers to lose proprietary information, suffer data corruption, lose operational capacity or fail to comply with applicable privacy and other laws. Among other potentially harmful effects, cyber incidents also may result in theft, unauthorized monitoring and failures in the physical infrastructure or operating systems that support the Fund and its service providers. In addition, substantial costs may be incurred in order to prevent any cyber incidents in the future. While the Fund’s service providers have established business continuity plans in the event of, and risk management systems to prevent, such cyber incidents, there are inherent limitations in such plans and systems including the possibility that certain risks have not been identified. Furthermore, the Fund cannot control the cybersecurity plans and systems put in place by its service providers or any other third parties whose operations may affect the Fund.

Certain Affiliations

Certain broker-dealers may be considered to be affiliated persons of the Fund, Nuveen Fund Advisors, Nuveen Asset Management, Nuveen and/or TIAA. Absent an exemption from the SEC or other regulatory relief, the Fund generally is precluded from effecting certain principal transactions with affiliated brokers, and its ability to purchase securities being underwritten by an affiliated broker or a syndicate including an affiliated broker, or to utilize affiliated brokers for agency transactions, is subject to restrictions. The Fund has not applied for and does not currently intend to apply for such relief. This could limit the Fund’s ability to engage in securities transactions and take advantage of market opportunities. In addition, unless and until the underwriting syndicate is broken in connection with the initial public offering of the Common Shares, the Fund will be precluded from effecting principal transactions with brokers who are members of the syndicate.

Unrated Securities Risk

The Fund may purchase securities that are not rated by any rating organization. Nuveen Asset Management may, after assessing such securities’ credit quality, internally assign ratings to certain of those securities in categories similar to those of rating organizations. Some unrated securities may not have an active trading market or may be difficult to value, which means the Fund might have difficulty selling them promptly at an acceptable price. To the extent that the Fund invests in unrated securities, the Fund’s ability to achieve its investment objective will be more dependent on Nuveen Asset Management’s credit analysis than would be the case when the Fund invests in rated securities.

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Risks in Valuation

The Fund utilizes independent pricing services approved by the Board to value portfolio instruments at their market value. If the pricing services are unable to provide a market value or if a significant event occurs such that the valuation(s) provided are deemed unreliable, the Fund may value portfolio instrument(s) at their fair value, which is generally the amount an owner might reasonably expect to receive upon a current sale. Valuation risks associated with investing in below investment grade debt instruments including, but not limited to: a limited number of market participants, a lack of publicly-available information, resale restrictions, settlement delays, corporate actions and adverse market conditions may make it difficult to value or sell such instruments. Because non-U.S. instruments may trade on days when Common Shares are not priced or traded, NAV can change at times when Common Shares cannot be sold.

Asset Segregation Risk

Certain portfolio management techniques, such as, among other things, using reverse repurchase agreements, purchasing investments on a when-issued or delayed delivery basis or entering into swap agreements, futures contracts or other derivative transactions, create leverage or its effect, and may be considered “senior securities’” (as that term is defined under the 1940 Act). To avoid having these instruments considered “senior securities,” the Fund may maintain liquid assets with its custodian in an amount with a value at least equal (on a daily market value basis or notional value basis, as applicable) to the aggregate amount of its obligations under these types of leveraging transactions (often referred to as “asset segregation”), enter into offsetting transactions, or otherwise “cover” certain transactions, in accordance with the 1940 Act, the rules thereunder, and applicable positions of the SEC and its staff. The SEC recently adopted new Rule 18f-4 under the 1940 Act, which, among other things, replaces the asset segregation framework previously used by funds to comply with Section 18 of the 1940 Act. The Fund will comply with the new rule’s requirements on or before the rule’s compliance date in 2022. See “Portfolio Composition and Other Information—Asset Segregation” above. In the event that the Fund is unable to maintain sufficient assets, or otherwise “cover,” any open positions, a portion or all of these instruments will be classified as a “senior security” for 1940 Act purposes and be subject to certain limitations on “senior securities” under the 1940 Act. See “Leverage” above. The Fund may be restricted in its use of assets that are maintained for “asset segregation,” or committed as “cover,” for certain other purposes, which could result in the Fund earning a lower return on its portfolio than it might otherwise earn if it did not have to maintain those assets in respect of, or otherwise “cover,” such portfolio positions. To the extent the Fund’s assets are maintained or committed as “cover,” it could limit the Fund’s investment flexibility. Maintaining assets and covering positions will not limit or offset losses on the related leveraging positions.

Counterparty Risk

The Fund will be subject to credit risk with respect to the counterparties to the derivative transactions entered into by the Fund. Changes in the credit quality of the companies that serve as the Fund’s counterparties with respect to derivatives transactions may affect the value of those instruments. Because certain derivative transactions in which the Fund may engage may be traded between counterparties based on contractual relationships, the Fund is subject to the risk that a counterparty will not perform its obligations under the related contracts. If a counterparty becomes bankrupt or otherwise becomes unable to perform its obligations due to financial difficulties the Fund

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may sustain losses (including the full amount of its investment), may be unable to liquidate a derivatives position or may experience significant delays in obtaining any recovery in bankruptcy or other reorganization proceedings. By entering into derivatives transactions, the Fund assumes the risk that its counterparties could experience such financial hardships. Although the Fund intends to enter into transactions only with counterparties that Nuveen Fund Advisors believes to be creditworthy, there can be no assurance that a counterparty will not default and that the Fund will not sustain a loss on a transaction. In the event of a counterparty’s bankruptcy or insolvency, any collateral posted by the Fund in connection with a derivatives transaction may be subject to the conflicting claims of that counterparty’s creditors, and the Fund may be exposed to the risk of a court treating the Fund as a general unsecured creditor of the counterparty, rather than as the owner of the collateral.

The counterparty risk for cleared derivatives is generally lower than for uncleared OTC derivative transactions. In a cleared derivative transaction, generally, a clearing organization becomes substituted for each counterparty to a cleared derivative contract and each party to a trade looks only to the clearing organization for performance of financial obligations under the derivative contract. In effect, the clearing organization guarantees a party’s performance under the contract. However, there can be no assurance that a clearing organization, or its members, will satisfy its obligations to the Fund, or that the Fund would be able to recover the full amount of assets deposited on its behalf with the clearing organization in the event of the default by the clearing organization or the Fund’s clearing broker. In addition, cleared derivative transactions benefit from daily marking-to-market and settlement, and segregation and minimum capital requirements applicable to intermediaries. Uncleared OTC derivative transactions generally do not benefit from such protections. As a result, for uncleared OTC derivative transactions, there is the risk that a counterparty will not settle a transaction in accordance with its terms and conditions because of a dispute over the terms of the contract (whether or not bona fide) or because of a credit or liquidity problem, thus causing the Fund to suffer a loss. This risk is heightened for contracts with longer maturities where events may intervene to prevent settlement, or where the Fund has concentrated its transactions with a single or small group of counterparties.

Risks Related to the Fund’s Clearing Broker and Central Clearing Counterparty

The CEA requires swaps and futures clearing brokers registered as “futures commission merchants” to segregate all funds received from customers with respect to any orders for the purchase or sale of U.S. domestic futures contracts and cleared swaps from the brokers’ proprietary assets. Similarly, the CEA requires each futures commission merchant to hold in separate secure accounts all funds received from customers with respect to any orders for the purchase or sale of foreign futures contracts and cleared swaps and segregate any such funds from the funds received with respect to domestic futures contracts. However, all funds and other property received by a clearing broker from its customers are held by the clearing broker on a commingled basis in an omnibus account and may be invested in certain instruments permitted under applicable regulations. There is a risk that assets deposited by the Fund with any swaps or futures clearing broker as margin for futures contracts or cleared swaps may, in certain circumstances, be used to satisfy losses of other clients of the Fund’s clearing broker. In addition, the assets of the Fund might not be fully protected in the event of the Fund’s clearing broker’s bankruptcy, as the Fund would be limited to recovering only a pro rata share of all available funds segregated on behalf of the clearing broker’s customers for the relevant account class.

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Similarly, the CEA requires a clearing organization approved by the CFTC as a derivatives clearing organization to segregate all funds and other property received from a clearing member’s clients in connection with domestic cleared derivative contracts from any funds held at the clearing organization to support the clearing member’s proprietary trading. Nevertheless, all customer funds held at a clearing organization in connection with any futures contracts are held in a commingled omnibus account and are not identified to the name of the clearing member’s individual customers. All customer funds held at a clearing organization with respect to cleared swaps of customers of a clearing broker are also held in an omnibus account, but CFTC rules require that the clearing broker notify the clearing organization of the amount of the initial margin provided by the clearing broker to the clearing organization that is attributable to each customer. With respect to futures and options contracts, a clearing organization may use assets of a non-defaulting customer held in an omnibus account at the clearing organization to satisfy payment obligations of a defaulting customer of the clearing member to the clearing organization. With respect to cleared swaps, a clearing organization generally cannot do so, but may do so if the clearing member does not provide accurate reporting to the clearing organization as to the attribution of margin among its clients. Also, since clearing brokers generally provide to clearing organizations the net amount of variation margin required for cleared swaps for all of its customers in the aggregate, rather than the gross amount of each customer, the Fund is subject to the risk that a clearing organization will not make variation margin payments owed to the Fund if another customer of the clearing member has suffered a loss and is in default. As a result, in the event of a default or the clearing broker’s other clients or the clearing broker’s failure to extend its own funds in connection with any such default, the Fund may not be able to recover the full amount of assets deposited by the clearing broker on behalf of the Fund with the clearing organization.

Portfolio Turnover Risk

The Fund’s annual portfolio turnover rate may vary greatly from year to year, as well as within a given year. The portfolio turnover rate is not considered a limiting factor in the execution of investment decisions for the Fund. High portfolio turnover may result in the realization of net short-term capital gains by the Fund which, when distributed to Shareholders, will be taxable as ordinary income. In addition, a higher portfolio turnover rate results in correspondingly greater brokerage and other transactional expenses that are borne by the Fund.

Rating Agencies Risk

Rating agencies may fail to make timely changes in credit ratings and an issuer’s current financial condition may be better or worse than a rating indicates. In addition, rating agencies are subject to an inherent conflict of interest because they are often compensated by the same issuers whose securities they grade.

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FINANCIAL HIGHLIGHTS

The following Financial Highlights table is intended to help a prospective investor understand the Fund’s financial performance for the periods shown. Certain information reflects financial results for a single Common Share of the Fund. The total returns in the table represent the rate an investor would have earned or lost on an investment in Common Shares of the Fund (assuming reinvestment of all dividends). The Fund’s annual financial statements and financial highlights as of and for the fiscal years ended March 31, 2020, 2019, 2018, 2017, 2016 and 2015, including the financial highlights for the fiscal years then ended, have been audited by KPMG LLP (“KPMG”), an independent registered public accounting firm. KPMG has not reviewed or examined any records, transactions or events after the date of such reports. The information with respect to the fiscal periods ended prior to March 31, 2015 has been audited by other auditors. The information with respect to the six months ended September 30, 2020 is unaudited and is included in the Fund’s 2020 Semi-Annual Report which is incorporated herein by reference. A copy of the Fund’s Annual and Semi-Annual Reports may be obtained from www.sec.gov or by visiting www.nuveen.com. The information contained in, or that can be accessed through, the Fund’s websites is not part of this prospectus, except to the extent specifically incorporated by reference in the SAI. Past results are not indicative of future performance.

The following per share data and ratios have been derived from information provided in the financial statements.

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Selected data for a Common Share outstanding throughout each period:

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THE FUND

The Fund is a diversified, closed-end management investment company registered under the 1940 Act. The Fund was organized as a Massachusetts business trust on December 4, 2009, pursuant to the Declaration of Trust, which is governed by the laws of the Commonwealth of Massachusetts. The Fund’s Common Shares are listed on the NYSE under the symbol “NBB.” The Fund’s principal office is located at 333 West Wacker Drive, Chicago, Illinois 60606, and its telephone number is (312) 917-7700.

5% Shareholders

As of December 31, 2020, no shareholders owned of record, or were known by the Fund to own of record or beneficially, five percent or more of any class of shares of the Fund.